Numerous examples of oncogenic viruses exist in nature. Concern has arisen that these viruses may pose a significant health risk to scientists studying them. At present, little data exist with which to evaluate this risk. The proposed project is designed to help elucidate this question by means of a retrospective case-control study utilizing the membership lists provided by several scientific organizations. The cases will be composed of scientists dying from cancer. The matched controls will be of two types--living scientists and scientists dying from causes of death thought to be unrelated to viruses. The factor of interest will be history of previous occupational viral exposure in a laboratory setting. A self-administered questionnaire and telephone interviews will be used for data collection. Analysis will be in keeping with the matched set design.